a. Field of the Invention
Generally, the present invention is related to the field of catheters. More particularly, aspects of the present invention relate to the field of catheter maneuvering and shaping, and to a catheter that employs fluid force to steer and change the shape of the catheter. Aspects of the present invention are also related to the field of ablation catheters, and more particularly to an ablation catheter manifolding arrangement for directing ablation fluid to a target tissue. Aspects of the present invention also involve electrode arrangements for ablation catheters, and more particularly an ablation catheter employing a continuous or partially continuous electrode adapted to provide a circumferential or partially circumferential lesion at a target vein.
b. Background Art
Catheters have been in use for medical procedures for many years. Catheters can be used for medical procedures to examine, diagnose, and treat while positioned at a specific location within the body that is otherwise inaccessible without more invasive procedures. During these procedures a catheter is inserted into a vessel located near the surface of a human body and is guided to a specific location within the body for examination, diagnosis, and treatment. For example, one procedure often referred to as “catheter ablation” utilizes a catheter to convey an electrical energy to a selected location within the human body to create necrosis, which is commonly referred to as ablation of cardiac tissue. Another procedure oftentimes referred to as “mapping” utilizes a catheter with sensing electrodes to monitor various forms of electrical activity in the human body.
Catheters are used increasingly for medical procedures involving the human heart. As illustrated in FIG. 1, a typical human heart 10 includes a right ventricle 12, a right atrium 14, a left ventricle 16 and a left atrium 18. The right atrium is in fluid communication with the superior vena cava 20 and the inferior vena cava 22. The interatrial septum 24 separates the right atrium from the left atrium. The tricuspid valve 26 contained within the atrioventricular septum provides a fluid flow path between the right atrium with the right ventricle. On the inner wall of the right atrium where it is connected with the left atrium is a thin walled, recessed area, referred to as the fossa ovalis 28. Between the fossa ovalis and the tricuspid valve is the opening or ostium for the coronary sinus 30. The coronary sinus is the large epicardial vein which accommodates most of the venous blood which drains from the myocardium into the right atrium.
In a normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electrochemical signals pass sequentially through the myocardium from the sinoatrial (SA) node (not shown) located in the right atrium to the atrialventricular (AV) node (not shown) and then along a well defined route which includes the His-Purkinje system into the left and right ventricles. Initial electric impulses are generated at the SA node and conducted to the AV node. The AV node lies near the ostium of the coronary sinus in the interatrial septum in the right atrium. The His-Purkinje system begins at the AV node and follows along the membranous interatrial septum toward the tricuspid valve 26 through the atrioventricular septum and into the membranous interventricular septum. At about the middle of the interventricular septum, the His-Purkinje system splits into right and left branches which straddle the summit of the muscular part of the interventricular septum.
Sometimes abnormal rhythms occur in the atrium which are referred to as atrial arrhythmia. Three of the most common arrhythmia are ectopic atrial tachycardia, atrial fibrillation and atrial flutter. Atrial fibrillation can result in significant patient discomfort and even death because of a number of associated problems, including the following: (1) an irregular heart rate, which causes a patient discomfort and anxiety, (2) loss of synchronous atrioventricular contractions which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure, and (3) stasis of blood flow, which increases the vulnerability to thromboembolism. It is sometimes difficult to isolate a specific pathological cause for the atrial fibrillation although it is believed that the principal mechanism is one or a multitude of stray circuits within the left and/or right atrium. These circuits or stray electrical signals are believed to interfere with the normal electrochemical signals passing from the SA node to the AV node and into the ventricles. Efforts to alleviate these problems in the past have included significant usage of various drugs. In some circumstances drug therapy is ineffective and frequently is plagued with side effects such as dizziness, nausea, vision problems, and other difficulties.
An increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia and atrial arrhythmia involves the ablation of tissue in the heart to cut off the path for stray or improper electrical signals. Such procedures are performed many times with an ablation catheter. Typically, the ablation catheter is inserted in an artery or vein in the leg, neck, or arm of the patient and threaded, sometimes with the aid of a guidewire or introducer, through the vessels until a distal tip of the ablation catheter reaches the desired location for the ablation procedure in the heart. The ablation catheters commonly used to perform these ablation procedures produce lesions and electrically isolate or render the tissue non-contractile at particular points in the cardiac tissue by physical contact of the cardiac tissue with an electrode of the ablation catheter and application of energy. The lesion partially or completely blocks the stray electrical signals to lessen or eliminate atrial fibrillations.
In some conventional ablation procedures, the ablation catheter includes a single distal electrode secured to the tip of the ablation catheter to produce small lesions wherever the tip contacts the tissue. To produce a linear lesion, the tip may be dragged slowly along the tissue during energy application. Increasingly, however, cardiac ablation procedures utilize multiple electrodes affixed to the catheter body to form multiple lesions.
One difficulty in obtaining an adequate ablation lesion using conventional ablation catheters is the constant movement of the heart, especially when there is an erratic or irregular heart beat. Another difficulty in obtaining an adequate ablation lesion is caused by the inability of conventional catheters to obtain and retain uniform contact with the cardiac tissue across the entire length of the ablation electrode surface. Without such continuous and uniform contact, any ablation lesions formed may not be adequate.
Moreover, effective ablation procedures are sometimes quite difficult because of the need for an extended linear lesion, sometimes as long as about three inches to five inches (approximately eight centimeters to twelve centimeters). To consistently produce such a linear lesion of this length within a wide variety of cardiac anatomies. In some instances, stray electrical signals find a pathway down the pulmonary veins 32 and into the left atrium. In these instances, it may be desirable to produce a circumferential lesion at the ostium 34 to one or more of the pulmonary veins or within one or more of the pulmonary veins. The pulmonary veins may reach a circumference of up to about 90 millimeters; thus, about a 90 millimeter circumferential lesion would be desirable to completely block stray signals from traveling down the pulmonary vein and into the left atrium.
Besides the difficulty in achieving an adequate lesion at the target tissue, it is also difficult to properly guide the catheter through the body to the target tissue and to change the shape of the catheter so that the ablation electrode is properly positioned at or against the target tissue. For instance, to guide a catheter into the left atrium of the heart for an ablation procedure at a pulmonary vein, a catheter oftentimes is fed into a vein in the right leg routed up to the right atrium of the heart, turned to the right and pressed through the septum between the left and right atrium to gain access to the left atrium. Once in the left atrium, the catheter must be further maneuvered to the appropriate pulmonary vein. In such a maneuvering of the catheter, numerous turns must be achieved to place the catheter at the ultimate target vein.